Known in the art is a method of expanding tubes in a tube wall by acting thereupon with a roller-type rolling tool and controlling a preselected varying effort associated with the expanding, e.g. the torque applied to the tool.
The method has a disadvantage resulting from the varying effort of the expanding of a tube being preselected and taken to be the same for all the tubes of a given heat exchanger or a group of heat exchangers with similar sizes and types of the tubes and of the tube sheets, without provision for individual properties of each rolling joint, which, however, have been found to vary within a significant range.
Consequently, the preselected effort is to be determined, in order to preclude "overrolling", for tubes with the most undesirable spread of mechanical properties and dimensions (the minimum yield point, the minimum tube sheet thickness, etc.).
Known in the art are expanding machines capable of performing the abovedescribed known method, such as the expanding machine marketed by Ferrometal in the Federal Republic of Germany, comprising a roller-type rolling tool associated with a drive and a device for measuring the torque applied to the tool, by the current consumed by the electric motor of the drive, and also a unit controlling this drive and terminating the expanding operation upon the value of the torque, i.e. of the current, having attained the predetermined magnitude.
By this method of expanding it is possible to ensure the maximum full strength and fluid-tightness of the rolling joint merely for a fraction of the total bulk of tubes, about 1 to 2 percent. The rest of the tubes have their potential load-bearing capacity underemployed, which results in inadequate reliability of rolling joints, production losses on account of downtime of the heat exchangers, and sometimes even to fires, explosions, and environment pollution.